AbstractPlant community productivity can increase with increasing intraspecific genotypic diversity. Previous studies have attributed the genetic diversity–productivity pattern to differential resource use among genotypes, as many studies have found for species. But here we ask whether suppression of productivity at low intraspecific diversity by soil biota might also drive a positive diversity–productivity relationship. In a previous study, we manipulated genetic diversity by varying the number of Pseudoroegneria accessions growing together in common garden plots, and used soil from that experiment to evaluate soil feedbacks. The total biomass of P. spicata plants grown in unsterilized soil increased with accession richness, specifically when comparing soil that had contained plants from 3 accessions to soil that had contained plants from either 8 or 12 population accessions. Furthermore, soil from high‐richness (8 or 12‐accession) plots drove neutral feedbacks, whereas soil in the 3‐accession plots (3) drove negative feedbacks. However, within each level of richness, there was no relationship between relative yield and feedback. Our results suggest that soil biota might play an integral role in the emerging understanding of the relationship between intraspecific diversity and ecosystem productivity.